1. Field of the Invention
The present invention relates to headlights, and more particularly to a headlight reduced in size while maintaining high efficiency.
2. Description of the Background Art
Conventional headlights have been configured as follows.
(a) Light emitted from a filament placed near the focal point of a parabolic mirror is reflected by the parabolic mirror to form a collimated beam. A front lens adjusts the collimated beam to attain a desired luminous intensity (or light) distribution pattern.
(b) Light emitted from a filament is received at a multi-surface mirror, which reflects the light frontward in a desired light distribution pattern. A front lens simply serves as a cover. Each portion of the multi-surface mirror has a size and angular arrangement determined to reflect the light incident from the filament in a predetermined direction such that the desired light distribution pattern is attained in their entirety.
One of the most critical issues regarding the headlight is its efficiency. In particular, in the case where a battery or the like is used as a power supply, high efficiency is pursued for a longer available time. Herein, the efficiency of the headlight is expressed as a ratio of luminous flux that has reached a target location with respect to the entire luminous flux radiated from a light bulb. In other words, the light that has arrived at locations other than the target location due to disturbance of distribution of the light, for example, is regarded as wasted light noncontributory to the efficiency.
A major stumbling block to downsizing of the headlight is degradation of the efficiency due to increased disturbance of light distribution. When the width and depth of the headlight are determined, the size of a reflector to be incorporated therein is determined. A filament is disposed near the focal point of the reflector. When the reflector is downsized and the focal distance is shortened, light emitted from portions of the filament off the focal point of the reflector may not be reflected as desired, thereby deteriorating the efficiency. More specifically, when the reflector is downsized, even if a filament of the same size is utilized, the degree of deviation of the portions of the filament off the focal point of the reflector increases, so that the disturbance of the light distribution is amplified correspondingly.
Such increase in disturbance of the light distribution due to the downsizing could be alleviated using a multi-surface mirror. However, the efficiency of the downsized headlight cannot be improved to a satisfactory level even if the multi-surface mirror is utilized. Accordingly, there has been a demand for development of a headlight reduced in size with the high efficiency being maintained.
An object of the present invention is to provide a downsized headlight with sufficiently high efficiency.
According to the present invention, a headlight projecting light frontward includes: a light source; a cylindrical condenser lens that surrounds the light source from its periphery and transmits light incident from the light source; and a reflector that surrounds the light source and the cylindrical condenser lens from their backsides and reflects the light transmitted through the cylindrical condenser lens frontward.
The cylindrical condenser lens is arranged to prevent divergence of the light emitted from the light source. Specifically, the light radiated from the light source sideward is received at the cylindrical condenser lens and is restricted in the degree of divergence before being directed to the reflector. Accordingly, when luminous flux of the same quantity is being emitted from the light source sideward, with provision of the cylindrical condenser lens, it becomes possible to reduce the height of the reflector in its axial direction, and hence to reduce the diameter thereof at its front end. More specifically, to reflect luminous flux of the same quantity without provision of the cylindrical condenser lens, a reflector would be required which covers an area up to a crossing point with an extended line of the line connecting the light source and a position where the front end of the cylindrical condenser lens is supposed to be located. Herein, this extended line is called a xe2x80x9cdownsizing reference linexe2x80x9d. With the provision of the cylindrical condenser lens, the reflector is only required to cover the back of the light source and the condenser lens up to the front end of the condenser lens. The light restricted in divergence is thus reflected frontward.
As a result, it is possible to considerably reduce the size of the reflector without degrading the efficiency. Here, the light source may be any kinds of illuminators, including a light bulb having a filament, a light-emitting diode and others.
Preferably, the cylindrical condenser lens of the headlight of the present invention is a cylindrical convex lens.
Arrangement of the cylindrical convex lens makes it possible to turn the light emitted from the light source into a light beam restricted in the degree of divergence.
Still preferably, the cylindrical convex lens concentrates the incident light as a parallel beam.
If the light restricted in divergence forms the parallel beam, it becomes easier to design the surface of the reflector reflecting the light frontward. This allows downsizing and also facilitates designing of the light distribution pattern with the reflector. Such a parallel beam can be obtained from the light transmitted through the cylindrical convex lens by positioning the light source at the focal point of the cylindrical convex lens.
Still preferably, the cylindrical convex lens is a Fresnel lens of a cylindrical shape.
Provision of the Fresnel lens allows reduction of the lens thickness. This leads to more compact configuration of the cylindrical convex lens around the light source and of the reflector, contributing to further downsizing of the headlight.
Preferably, the reflector of the headlight of the present invention is a multi-surface mirror.
Using the multi-surface mirror, it is possible to obtain a wide variety of frontward light distribution patterns, from which a predetermined pattern can be selected and set.
Preferably, the headlight of the present invention is provided with a front lens in front of the light source. The front lens preferably includes at least two portions having light transmission characteristics different from each other.
Provision of the portions having different light transmission characteristics enables meticulous designing of the light distribution patterns with the front lens. The light transmission characteristic of each portion of the front lens can be determined by adjusting the thickness, curvatures of both surfaces and refractive index of the relevant portion. With the headlight reduced in size as described above, even if the center lens is small in size, the solid angle at the light source encompassing the center lens becomes large. Accordingly, it is possible to increase influence of the center lens on the light distribution pattern.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.